POS0276 TRADITION VS INNOVATION! CONVENTIONAL RADIOGRAPHY AND ULTRASOUND IN THE DIAGNOSIS OF CPPD: INSTRUCTIONS FOR USE
Authors: S. Sirotti, F. Becce, L. M. Sconfienza, L. Terslev, A. Zanetti, E. Naredo, P. Zufferey, M. Gutierrez, A. Adinolfi, T. Serban, D. Maccarter, G. Mouterde, A. Scanu, I. Möller, C. A. Scirè, P. Sarzi-Puttini, U. Novo-Rivas, A. Abhishek, H. Choi, N. Dalbeth, S. Tedeschi, A. Iagnocco, C. Pineda, H. Keen, M. A. D’agostino, G. Filippou
Journal: Annals of the Rheumatic Diseases (2022)

Background Conventional radiography (CR) is widely used as the first-line investigation for calcium pyrophosphate deposition (CPPD) disease, given its widespread use and the low cost. Next to it a series of advanced imaging techniques have been evaluated for accuracy and reliability. Among them, ultrasound (US) has been thoroughly tested and demonstrated to be accurate and reliable for CPPD diagnosis. However, even if there are data on the diagnostic accuracy of US and CR alone, it is not clear if performing both diagnostic tests and in which sequential order provides an added value for the diagnosis of CPPD. Objectives The aim of this study was to assess which diagnostic test performs better for the diagnosis of CPPD and if a combination of the two exams provides an additional value. Methods This is an ancillary study of the criterion validity of US in CPPD study 1 . Consecutive patients with knee osteoarthritis requiring total joint replacement were enrolled in 8 centres. Participants underwent US and CR of the affected knee prior to surgery. US was performed by experienced sonographers following the same scanning protocol described in the main study, while CR were performed in weight bearing AP and lateral views and were read by 2 experienced radiologists that reached a consensus on the presence/absence of CPPD. The evaluation of CPPD at the level of menisci and hyaline cartilage (HC) was based on the OMERACT definitions for US and on the new definitions developed by the ACR/EULAR CPPD classification criteria working group for CR [paper under submission]. Patients were classified as having CPPD considering histological examination as reference standard. Diagnostic indexes were calculated for US and CR alone and combined. Poisson models with robust estimation were used to estimate the best sequence of these diagnostic methods for a more accurate diagnosis of CPPD. Results 51 pts were enrolled (63% F, mean age 74y ± 8). Diagnostic indexes of US and CR alone and combined are indicated in Table 1. Compared to histology, US demonstrated to be a sensitive tool for identification of CPPD at the knee, with a good sensitivity in all sites and in the overall evaluation. Instead, CR was less sensitive, but it was a highly specific exam for CPPD identification. Combining US and CR led to a higher sensitivity compared with CR alone, but a lower specificity compared to both CR and US alone, and it offered no additional increase in diagnostic accuracy. The Figure 1 shows the results of the appropriate sequence of use of US and CR in patients with suspected CPPD: in case of a positive CR at any of the 3 sites (menisci and HC) no additional exam is necessary, and the same in case of a positive US in at least two sites; however in case of a negative CR, US could help in a statistically significant way to identify CPPD patients, and further in case of a positive US in a single site CR can offer additional information. Table 1. diagnostic indexes of US, CR and US + CR in the identification of CPPD. MM: medial meniscus, LM: lateral meniscus, HC: hyaline cartilage, SN: sensitivity, SP: specificity, PPV: positive predictive value, NPV: negative predictive value, ACC: accuracy. US SN SP PPV NPV ACC MM 0.88 0.81 0.82 0.88 0.84 LM 0.88 0.73 0.76 0.86 0.80 HC 0.78 0.86 0.82 0.83 0.82 Overall 0.92 0.64 0.73 0.89 0.78 CR MM 0.32 1 1 0.61 0.67 LM 0.40 0.96 0.91 0.63 0.69 HC 0.48 0.93 0.85 0.68 0.73 Overall 0.54 0.92 0.88 0.66 0.73 US + CR MM 0.88 0.81 0.82 0.88 0.84 LM 0.92 0.69 0.74 0.90 0.80 HC 0.87 0.82 0.80 0.89 0.84 Overall 0.92 0.56 0.67 0.88 0.75 Figure 1. evaluation of sequence of US and CR Conclusion US confirmed a high diagnostic accuracy in identifying patients affected by CPPD at knee level, while CR demonstrated a high specificity but a low sensitivity. Performing both diagnostic tests could make sense in case of a negative CR or in case of an inconclusive US (only one positive site). To our knowledge, this is the first study that investigates the role of the combination of the two exams in CPPD. Further studies in a large number of patients and in different joints would be helpful to address this point. References [1]Filippou G. et al, Ann Rheum Dis, 2020 Disclosure of Interests None declared